How to Build a Raised Deck

A raised deck attached to a house almost universally requires a building permit, and most jurisdictions also require engineered structural drawings when the deck exceeds 30 inches above grade. The permit process is not optional — it protects the structure legally, keeps your homeowner's insurance valid, and documents the work for future buyers. Permits typically cost $75–$250 and take 1–3 weeks. Before designing anything, call your building department and ask for the local frost depth, required footing diameter, and approved ledger attachment method. These three answers drive which products you buy. Get HOA approval in writing if applicable, and call 811 at least 3 business days before digging to have underground utilities marked.

Batter boards are temporary reference frames set 2 ft outside each deck corner that let you re-establish string lines after digging without losing your layout. A raised deck at 42 in carries significantly more load than a ground-level deck, so footing placement precision matters more — an off-centre footing shifts the post, the beam, and every joist above it. Stretch string lines between batter boards and confirm square using the 3-4-5 triangle: 3 ft along one string, 4 ft along the perpendicular — the diagonal must be exactly 5 ft. Scale up to 9-12-15 for a full deck perimeter check. Measure both diagonals; they must be equal within ¼ in. Drop a plumb bob from each string intersection to mark footing centres on the ground.

Raised deck footings must go below the local frost line — the depth at which ground freezes. Soil that freezes and heaves will move a footing, shifting every post, beam, and connection above it. For a deck over 30 in above grade, this is not a code suggestion; it is a structural requirement. Northern climates (Zone 5–7) typically require 42–48 in. Confirm with your building department. For 6×6 posts, use a minimum 16-in diameter footing — inspectors for raised decks commonly require this regardless of post size. Add a 6-in pea gravel drainage base before any concrete. Set tube forms so their tops sit 2–3 in above finished grade to keep surface water out of the footing.

Fill tube forms in 6-in lifts, tamping with a rod after each lift to eliminate air pockets. While the concrete is still wet, insert a post anchor centred in the pour and aligned to your string lines. For a raised deck with wind exposure, upgrade from a standard J-bolt to a Simpson ABU66Z or ABA66Z uplift anchor — these resist both downward load and upward wind forces that a simple J-bolt does not. Set the top of every anchor at least 1 in above finished grade so the post base sits clear of standing water. Let the concrete cure a minimum of 24 hours; 48 hours is preferred before applying any load. Check anchor alignment once more after initial set — you have about 20 minutes of workability in fast-setting mixes.

Cut 6×6 UC4B (In-Ground) posts to rough height — add 12 in above your target beam height so you can trim them perfectly level after the posts are plumbed. UC4B is required here because the posts are set in concrete; UC4A is only rated for post bases above grade. Set each post in its anchor, clamp a 4-sided post level to it, and brace with two 2×4 kickers at 90° to each other, staked to the ground. Plumb in both directions. Do not fully torque the anchor hardware until all posts are braced — you need the ability to fine-tune. The post top must be at the underside of the beam; the beam bears on top of the post, not alongside it.

The ledger carries half the deck load and is the primary water intrusion risk on any attached deck. Remove house siding entirely from the ledger zone before starting — never install a ledger over siding, foam sheathing, or any non-structural veneer. Apply Vycor Plus self-adhering membrane to the exposed band joist, extending at least 2 in above and below the ledger zone. Attach the ledger with FastenMaster LedgerLOK screws in two staggered rows at 16-in o.c. per IRC Table R507.9.1.3 — no pre-drilling needed, and they are ICC code-compliant without the splitting risk of traditional ½-in lag bolts. Once the ledger is fastened, install Z-flashing over its top edge tucking the upper flange under the siding above, then seal every fastener penetration and flashing overlap with exterior silicone.

Build the doubled 2×10 UC3B beam by face-nailing two boards together with 16d HDG nails at 16-in o.c. in two staggered rows. Crown-check each board first and orient both plies crown-side up. Set the assembled beam on top of the posts and secure with AC6Z or BC6 ZMAX post caps — saddle caps provide the strongest post-to-beam connection. Install 2×8 UC3B rim joists to define the deck perimeter, attaching to both the beam and the ledger with 3-in structural screws at 12-in o.c. Crown every rim joist up so the finished deck surface is slightly convex for water shedding. Check both diagonals of the frame before moving on — they must be equal within ¼ in. Apply butyl joist tape to the top edge of all rim joists.

Install 2×8 UC3B interior joists at 16-in o.c. using Simpson LUS28Z ZMAX hangers. Snap chalk lines on both the ledger and the opposite rim at 16-in intervals, marking the waste side of each line so all joists land consistently. Position every hanger with its top flush with the ledger top — a hanger set even ¼ in low creates a bump in the finished surface. Fill every nail hole in every hanger with 10d × 1½-in HDG joist hanger nails — this is the most commonly failed item on deck framing inspections. Install an H2.5AZ hurricane tie at each joist-to-rim junction. For spans over 8 ft, install solid blocking at mid-span. Apply butyl joist tape across the full top surface of every joist before decking.

Lay 2×6 UC3B (Above Ground) deck boards starting from the ledger, working outward. UC3B is the correct and less expensive rating here — boards are the walking surface and never contact soil. Dry-lay 4–5 boards first to plan the run and determine whether the final board needs ripping. Drive two GRK Deck Elite 2-½-in screws per joist crossing, 1 in from each edge. The Zip-Tip self-pilots without pre-drilling except within 2 in of board ends. Use a 16d nail as a 1/8-in spacer between boards. Every 10 boards, snap a chalk line to confirm the run stays parallel to the house. When all boards are down, snap a line 1 in past the outer rim face and cut the entire overhang in one continuous saw pass. Apply end-cut preservative to every cut end within 30 minutes.

A deck at 42 in requires a stair assembly governed by IRC R311.7. The first task is calculating the actual total rise from finished deck surface to grade on-site — it is rarely exactly 42 in. Divide total rise by 7 in (the target riser height; maximum 7-¾ in per IRC R311.7.5.1) and round to determine the number of risers. Tread depth minimum is 10 in nosing-to-nosing (IRC R311.7.5.2). Stair width must be 36 in clear minimum. Cut 2×12 UC3B stringer blanks with a minimum 3-½ in of solid wood below every tread cut — the effective depth rule under IRC R311.7.6.1. Attach stringers to the rim joist with Simpson stringer angle brackets, minimum 2 structural bolts each. The stringer bottom must bear on a concrete pad, not on bare soil or grade.

At 42 in above grade, a 42-in-tall guardrail is required by IRC R312.1 on all open sides. Balusters must be spaced so a 4-in sphere cannot pass through any opening (IRC R312.1.3). Mount railing posts to the rim joist face with ½-in stainless carriage bolts through-bolted — screws alone are not permitted for post attachment. For the Trex Transcend system: mount line posts at ≤ 6-ft centres, install post sleeves and skirts to conceal hardware, cut and install bottom rail, insert balusters with a 4-in spacer block for consistent IRC-compliant spacing, then attach the top rail. Install the graspable stair handrail on the stair side per IRC R311.7.8.